Cancer remains a major public health challenge despite progress in detection and therapy. Amongst the various types of cancer, LC is a frequent cancer in the Western world and among the most frequent cause of cancer-related mortality. This is in large part due to the diagnostic gap for early detection of the disease. LC is largely asymptomatic in its early stages. The majority of all lung cancers is detected at a late stage when the disease has already become inoperable.
The majority of LC tumors can be divided into small cell lung carcinoma (SCLC) and non-small cell lung carcinoma (NSCLC). SCLC accounts for about 20-25% of all lung cancer cases. SCLC is an aggressive neuroendocrine type of LC and has a very poor prognosis even if detected in early stages. SCLC is rarely amenable to curative treatment by resection. Because of the speed with which the disease progresses, SCLC is generally categorized using only two stages, i.e., limited and extensive disease, rather than the more complex TNM staging system (see below). About 75-80% of LC cases are grouped into the class of NSCLC including squamous cell carcinoma (carcinoma=CA), adeno-CA (comprising the subclasses of acinar CA, papillary CA, bronchoalveolar tumor, solid tumor, and mixed subtypes), and large cell carcinoma (comprising the subclasses of giant cell tumors, clear cell CA, adenosquamous CA, and undifferentiated CA).
NSCLC, if detected at late stages, also has a very poor prognosis. The staging of cancer is the classification of the disease in terms of extent, progression, and severity. It groups cancer patients so that generalizations can be made about prognosis and the choice of therapy.
Today, the TNM system is the most widely used classification system based on the anatomical extent of cancer. It represents an internationally accepted, uniform staging system. There are three basic variables: T (the extent of the primary tumor), N (the status of regional lymph nodes) and M (the presence or absence of distant metastases). The TNM criteria are published by the UICC (International Union Against Cancer), in: TNM Classification of Malignant Tumours, fifth edition, Sobin, L. H. and Wittekind, Ch. (eds.), Wiley-Liss (1997), pp. 1803-1804)
Surgical resection of the primary tumor is widely accepted as the treatment of choice for early stage NSCLC. With the progression of NSCLC and, more specifically, the transition from stage IIIa (T3N1M0, T1N2M0, T2N2M0, T3N2M0) to IIIb (T4N0M0, T4N1M0, T4N2M0), a significant shift in the physician's approach is precipitated. However, if the cancer is detected during the more early stages (Ia-IIIa; preferably up to stage T3N1M0), the five-year survival rate varies between 35% and 80%. Detection at stage Ia ((T1N0M0); small tumor size, no metastasis) has evidently the best prognosis with a five-year survival of up to 80%.
Surgery is rarely, if ever, used in the management of stage IIIb-IV of NSCLC. Stage IV corresponds to distant metastasis, i.e., spread of the disease beyond the lungs and regional lymph nodes. The five-year survival rate in the later stages (III-IV) drops to between less than 1% and 15%.
What is especially important is that early diagnosis of NSCLC translates to a much better prognosis. Patients diagnosed as early as in stage Ia (T1N0M0), Ib (T2N0M0), IIa (T1N1M0), IIb, (T3N0M0), and IIIa (T3N1M0), if treated properly have an up to 80% chance of survival 5 years after diagnosis. This has to be compared to a 5-years survival rate of less than 1% for patients diagnosed once distant metastases are already present.
In the sense of the present invention early assessment of LC refers to an assessment at a tumor stage T1N0M0 or T1-3N0-1M0.
It is preferred that LC is assessed at stage T1-3N0-1M0 (=T1-3N0-M0).
Most lung cancers are detected when they become symptomatic. Current detection methods include chest x-ray, spiral computer tomography, sputum cytology and bronchioscopy. However, there is controversy regarding the suitability of these means for mass screenings.
A number of serum tumor markers for lung cancers are in clinical use. The soluble 30 kDa fragment of cytoceratin 19 (CYFRA 21-1), carcinoembryogenic antigen (CEA), neuron-specific enolase (NSE), and squamous cell carcinoma antigen (SCC) are the most prominent LC markers. However, none of them meets the criteria for sensitivity and specificity required for a screening tool (Thomas, L., Labor und Diagnose, TH Books Verlagsgesellschaft, Frankfurt/Main, Germany (2000)).
In order to be of clinical utility, a new diagnostic marker as a single marker should be comparable to other markers known in the art, or better. Or, a new marker should lead to a progress in diagnostic sensitivity and/or specificity either if used alone or in combination with one or more other markers, respectively. The diagnostic sensitivity and/or specificity of a test is best assessed by its receiver-operating characteristics, which will be described in detail below.
Whole blood, serum or plasma are the most widely used sources of sample in clinical routine. The identification of an early LC tumor marker that would aid in the reliable cancer detection or provide early prognostic information could lead to a method that would greatly aid in the diagnosis and in the management of this disease. Therefore, an urgent clinical need exists to improve the in vitro assessment of LC. It is especially important to improve the early diagnosis of LC, since for patients diagnosed early on chances of survival are much higher as compared to those diagnosed at a progressed stage of disease.
The clinical utility of biochemical markers in lung cancer has recently been reviewed (Duffy, M. J., Crit. Rev. Clin. Lab. Sci. 38 (2001) 225-262).
CYFRA 21-1 is currently regarded to be the best of the presently known tumor markers for lung cancer. Even though not organ-specific it is predominantly found in lung tissue. Sensitivity of CYFRA 21-1 for lung cancer is described to be between 46-61% at a specificity of 95% towards other benign lung diseases. Increased serum levels of CYFRA 21-1 are also associated with pronounced benign liver diseases, renal insufficiency and invasive bladder cancer. CYFRA 21-1 testing is recommended for postoperative therapy surveillance.
CEA belongs to the group of carcinofetal antigens usually produced during embryogenesis. CEA is not organ-specific and predominantly used for monitoring of colorectal cancer. Besides malignancies, also several benign diseases such as cirrhosis, bronchitis, pancreatitis and autoimmune diseases are associated with increased CEA serum levels. At 95% specificity towards benign lung diseases its sensitivity for lung cancer is reported to be 29-44%. A preferred use of CEA is therapy surveillance of lung cancer.
NSE is a tumor marker for SCLC. Generally, increased NSE serum levels are found in association with neuroectodermal and neuroendocrine tumors. Increased serum levels are also found in patients with benign lung diseases and cerebral diseases, such as meningitis or other inflammatory diseases of the brain, and traumatic injuries to the head. While sensitivity for SCLC at 95% specificity is reported to be 60-87%, performance of NSE testing for NSCLC is poor (7-25%). NSE is recommended for therapy surveillance of SCLC.
SCC was originally identified in squamous cell CA of the cervix. The sensitivity of SCC for LC in general is low (18-27%). Therefore, SCC testing is regarded to be not suitable for screening. However, due to a higher sensitivity for squamous cell CA, a preferred use for SCC is therapy surveillance, even though CYFRA 21-1 generally performs better.
With respect to marker profiles and aiming at improved diagnosis of lung cancer, a method was published (Schneider, J. et al., Int. J. Clin. Oncol. 7 (2002) 145-151) using fuzzy logic based classification algorithms to combine serum levels of CYFRA 21-1, NSE and C-reactive protein (CRP) which is a general inflammation marker. The authors report a sensitivity of 92% at a specificity of 95%.
It was the task of the present invention to investigate whether a biochemical marker can be identified which may be used in assessing LC.
Surprisingly, it has been found that use of the marker NNMT can at least partially overcome some of the problems of the markers presently known in the state of the art.